1. Field of the Invention
The present invention relates to a valve opening degree control system and a common rail type fuel injection system.
2. Description of Related Art
A common rail type fuel injection system controls a rail pressure (a pressure of fuel accumulated in a common rail) by controlling a discharge rate of a high pressure pump to limit a reduction in the rail pressure caused by fuel injection or to increase the rail pressure according to an operational state. The discharge rate of the high pressure pump is controlled by adjusting or controlling an intake rate of fuel, which is drawn into a compression chamber of the high pressure pump, through use of an inlet metering valve.
More specifically, the common rail type fuel injection system controls the rail pressure by controlling the discharge rate of the high pressure pump through adjustment of a degree of opening of the inlet metering valve by a control device.
Thus, the discharge rate of the high pressure pump relative to a metering valve control value (a drive electric current value for achieving a predetermined degree of opening of the inlet metering valve), which is supplied to the inlet metering valve, should coincides with a predetermined pump characteristic.
However, the actual discharge rate of fuel, which is actually discharged from the high pressure pump, can possibly vary relative to the metering valve control value due to various factors, such as manufacturing variations and aging variations of the mass produced inlet metering valves, and/or variations in the temperature characteristics of, for example, a fuel viscosity or a coil attractive force.
To address the above disadvantages, for example, Japanese Unexamined Patent Publication No. 2001-82230 proposes the following learning control operation. In this learning control operation, when a predetermined learning condition is satisfied (e.g., when an engine is in an idling state), the degree of opening of the inlet metering valve is progressively increased from a prefixed value, at which a zero intake rate of the inlet metering valve is guaranteed. At the time of progressively increasing the degree of opening of the inlet metering valve from this value, when the amount of the change in the rail pressure becomes equal to or greater than a predetermined value, the current metering valve control value, which is currently supplied to the inlet metering valve, is obtained as an intake initiation control value. Then, this value (the intake initiation control value) is learned as a metering valve control value, at which the high pressure pump begins the intake of fuel. In this way, variations in the small discharge rate range of the high pressure pump (the small degree of opening of the inlet metering valve) are corrected.
When an opening cross sectional area variable valve, which varies its fuel passage opening cross sectional area, is used as a valve (corresponding to the inlet metering valve in the above case), accurate control of the passage opening cross sectional area of the valve between a small degree of opening and a large degree of opening is required. However, when the above technique recited in Japanese Unexamined Patent Publication No. 2001-82230 is applied to the learning control of the valve, the variation in the small degree of opening of the valve can be corrected, and the variation in the large degree of opening of the valve cannot be corrected.
Furthermore, when the opening cross sectional area variable valve is not used as the above valve, that is when a valve, which adjusts the degree of opening of the valve by adjusting a time period of opening (i.e., fully opening) the valve, is used, the variation is correctable only in the small degree of opening of the valve while disallowing correction of the variation in the large degree of opening of the valve.
For example, when the opening cross sectional area variable valve, which adjusts the passage opening cross sectional area of a fluid passage that conducts the fluid to the high pressure pump, is used as the inlet metering valve of the common rail type fuel injection system, accurate control of the opening cross sectional area of the fluid passage between the small degree of opening and the large degree of opening is required. However, the above technique recited in Japanese Unexamined Patent Publication No. 2001-82230 is intended to correct the variation in the small degree of opening of the inlet metering valve (a small discharge rate range of the high pressure pump) and cannot correct the variation in the large degree of opening of the inlet metering valve (a large discharge rate range of the high pressure pump).
Furthermore, when the opening cross sectional area variable valve is not used as the inlet metering valve, that is, when the valve, which adjusts the degree of opening of the valve by adjusting the time period of opening (i.e., fully opening) the valve, is used as the inlet metering valve, the variation is only correctable in the small degree of opening, and the variation in the large degree of opening is not correctable.
In some common rail type fuel injection systems, a pressure-reducing valve, which reduces the rail pressure by draining the fuel accumulated in the common rail, is provided.
When a predetermined condition for rapidly reducing the rail pressure, is satisfied due to a change in the operational state, a required degree of opening of the pressure-reducing valve, which corresponds to the required pressure to be decreased, is computed by the control device. Then, a pressure-reducing valve control value, which corresponds to the required degree of opening, is supplied to the pressure-reducing valve. Thus, the rail pressure is rapidly reduced to the target rail pressure by the pressure-reducing valve.
For example, when the opening cross sectional area variable valve, which adjusts the passage opening cross sectional area of a drain passage that drains the fluid accumulated in the common rail, is used as the pressure-reducing valve, accurate control of the opening cross sectional area of the drain passage between the small degree of opening and the large degree of opening is required. However, when the above technique recited in Japanese Unexamined Patent Publication No. 2001-82230 is used in the correcting operation of the pressure-reducing valve, the variation in the small degree of opening of the pressure-reducing valve can be corrected, and the variation in the large degree of opening of the pressure-reducing valve cannot be corrected.
Furthermore, when the opening cross sectional area variable valve is not used as the pressure-reducing valve, that is, when the valve, which adjusts the degree of opening of the valve by adjusting the time period of opening (i.e., fully opening) the valve, is used as the pressure-reducing valve, the variation is only correctable in the small degree of opening, and the variation in the large degree of opening is not correctable.